<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Document</title>
    <script src="../lib/vue.js"></script>
</head>
<body>
    <div id="app">
        <input type="text" v-model="n1"/>

        <select v-model="opt">
            <option value="+">+</option>
            <option value="-">-</option>
            <option value="*">*</option>
            <option value="/">/</option>
        </select>

        <input type="text" v-model="n2"/>

        <input type="button" value="=" @click="math"/>

        <input type="button" v-model="result"/>
    </div>

    <script>
        var vm = new Vue({
            el:'#app',
            data:{
                n1:0,
                n2:0,
                opt:'+',
                result:0
            },
            methods:{
                math() {
                    //var f = this.n1;
                    //var l = this.n2;
                    // switch(this.opt){
                    //     case '+': this.result = Number(f)+Number(l); break;
                    //     case '-': this.result = f-l; break;
                    //     case '*': this.result = f*l; break;
                    //     case '/': this.result = f/l
                    // }
                    var str = 'parseInt(this.n1)'+this.opt+'parseInt(this.n2)';
                    this.result = eval(str);
                }
            }
        })    
    </script>
</body>
</html>